[PATCH] Fix -Wreturn-type with -fsanitize=return (PR c++/81212)

[Jakub Jelinek]

Hi!

With -fsanitize=return, we add __builtin_ubsan_handle_missing_return
instead of __builtin_unreachable with BUILTINS_LOCATION locus,
the following patch teaches warn function return pass to handle that too.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2017-12-01  Jakub Jelinek  <ja...@redhat.com>

        PR c++/81212
        * tree-cfg.c (pass_warn_function_return::execute): Handle
        __builtin_ubsan_handle_missing_return like __builtin_unreachable
        with BUILTINS_LOCATION.

        * g++.dg/ubsan/pr81212.C: New test.
        * g++.dg/ubsan/return-1.C: Add -Wno-return-type to dg-options.
        * g++.dg/ubsan/return-2.C: Add -Wno-return-type to dg-options.
        * g++.dg/ubsan/return-7.C: Add -Wno-return-type to dg-options.

--- gcc/tree-cfg.c.jj   2017-12-01 09:10:12.000000000 +0100
+++ gcc/tree-cfg.c      2017-12-01 19:38:21.933049446 +0100
@@ -9151,10 +9151,13 @@ pass_warn_function_return::execute (func
          if (EDGE_COUNT (bb->succs) == 0)
            {
              gimple *last = last_stmt (bb);
+             const enum built_in_function ubsan_missing_ret
+               = BUILT_IN_UBSAN_HANDLE_MISSING_RETURN;
              if (last
-                 && (LOCATION_LOCUS (gimple_location (last))
-                     == BUILTINS_LOCATION)
-                 && gimple_call_builtin_p (last, BUILT_IN_UNREACHABLE))
+                 && ((LOCATION_LOCUS (gimple_location (last))
+                      == BUILTINS_LOCATION
+                      && gimple_call_builtin_p (last, BUILT_IN_UNREACHABLE))
+                     || gimple_call_builtin_p (last, ubsan_missing_ret)))
                {
                  gimple_stmt_iterator gsi = gsi_for_stmt (last);
                  gsi_prev_nondebug (&gsi);
--- gcc/testsuite/g++.dg/ubsan/pr81212.C.jj     2017-12-01 19:30:43.251747933 
+0100
+++ gcc/testsuite/g++.dg/ubsan/pr81212.C        2017-12-01 19:30:25.000000000 
+0100
@@ -0,0 +1,16 @@
+// PR c++/81212
+// { dg-do compile }
+// { dg-options "-Wreturn-type -fsanitize=return" }
+
+struct S
+{
+  S (void *);
+  void *s;
+};
+
+S
+foo (bool x, void *y)
+{
+  if (x)
+    return S (y);
+}      // { dg-warning "control reaches end of non-void function" }
--- gcc/testsuite/g++.dg/ubsan/return-1.C.jj    2013-11-22 21:05:59.000000000 
+0100
+++ gcc/testsuite/g++.dg/ubsan/return-1.C       2017-12-01 22:23:17.053866660 
+0100
@@ -1,5 +1,5 @@
 // { dg-do run }
-// { dg-options "-fsanitize=return" }
+// { dg-options "-fsanitize=return -Wno-return-type" }
 // { dg-shouldfail "ubsan" }
 
 struct S { S (); ~S (); };
--- gcc/testsuite/g++.dg/ubsan/return-2.C.jj    2014-10-22 15:52:16.000000000 
+0200
+++ gcc/testsuite/g++.dg/ubsan/return-2.C       2017-12-01 22:23:32.059679081 
+0100
@@ -1,5 +1,5 @@
 // { dg-do run }
-// { dg-options "-fsanitize=return -fno-sanitize-recover=return" }
+// { dg-options "-fsanitize=return -fno-sanitize-recover=return 
-Wno-return-type" }
 
 struct S { S (); ~S (); };
 
--- gcc/testsuite/g++.dg/ubsan/return-7.C.jj    2016-11-23 20:50:51.000000000 
+0100
+++ gcc/testsuite/g++.dg/ubsan/return-7.C       2017-12-01 22:24:03.894281135 
+0100
@@ -1,5 +1,5 @@
 // { dg-do run }
-// { dg-options "-fsanitize=undefined" }
+// { dg-options "-fsanitize=undefined -Wno-return-type" }
 // { dg-shouldfail "ubsan" }
 
 struct S { S (); ~S (); };

        Jakub